Image pickup tube

ABSTRACT

An image pickup tube, particularly for a color television camera, has an envelope closed, at one end, by a transparent faceplate which has a color filter on its inner surface made up of groups of stripe-shaped parallel filter regions passing respectively different wavelengths of light. A transparent glass plate is secured against the color filter and, at its surface remote from the filter, carries a pair of interleaved, combshaped electrodes having their respective elongated transparent element arranged alternately with a pitch equal to the pitch of the repeating cyclic order of the groups of color filter regions and extending parallel to the latter. A photoconductive layer covers at least the transparent elements of the comb-shaped electrodes, and output electrodes, preferably in the form of posts extending through the mentioned glass plate and faceplate, are respectively connected to the comb-shaped electrodes.

United States Patent [1 1 Kubota [451 Nov. 13, 1973 IMAGE PICKUP TUBE [75] Inventor: Yasuharu Kubota, Fujisawa-shi,

Japan [73] Assignee: Sony Corporation, Iqlryp tpa n 221 Filed: May 26,1972

211 App1.No.:257,41l

Related U.S. Application Data [62] Division of Ser. Nos. 72,593, Sept. 16, 1970, Pat. No.

3,668,020, and Ser. No. 176,553, Aug. 31, 1971.

[52] U.S. Cl 313/65 R, 313/66, 313/329 [51] Int. Cl. H0lj 31/26 [58] Field of Search 313/329, 65 R, 65 A [56] References Cited UNITED STATES PATENTS 11/1958 Fiore et a1. 313/65 A 3/1962 Weimer 313/65 A X 313/65 A X [5 7] ABSTRACT An image pickup tube, particularly for a color television camera, has an envelope closed, at one end, by a transparent faceplate which has a color filter on its inner surface made up of groups of stripe-shaped parallel filter regions passing respectively different wavelengths of light. A transparent glass plate is secured against the color filter and, at its surface remote from the filter, carries a pair of interleaved, comb-shaped electrodes having their respective elongated transparent element arranged alternately with a pitch equal to the pitch of the repeating cyclic order of the groups of color filter regions and extending parallel to the latter. A photoconductive layer covers at least the transparent elements of the comb-shaped electrodes, and output electrodes, preferably in the form of posts extending through the mentioned glass plate and faceplate, are respectively connected to the comb-shaped electrodes.

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F/G'. 7 I 32 33 IMAGE PICKUP TUBE continuation-in-part of said application Ser. No.

72,593, and both of which have a common assignee herewith.

This invention relates generally to image pickup tubes, and more particularly is directed to an image pickup tube which can be employed for producing a color video or television signal.

A pickup tube of the type having a target with a multiplicity of color filters and signal plates extending transversely of the direction of line scan has been disclosed in U.S. Pat. No. 2,446,249. In this type of pickup tube the signal plates corresponding to the color filters are connected to bus bars and the respective primary color video signals are derived from three signal output terminals connected to the bus bars. However, this pickup tube is defective in that each primary color video signal is mixed with other primary color video signals due to the electrostatic capacity coupling present between the respective signal electrodes. This results in crosstalk which lowers the color purity of the color video signal.

There has also been proposed a system, for example, as disclosed in U.S. Pat. No. 3,502,799, in which a plurality of index signal images and striped color component images are optically formed on the target of a vidicon tube to produce a composite color video signal with an index. With this system, however, the ratio between the color component image area and the efi'ective scanning area of the vidicon is decreased by an amount corresponding to the area occupied by the index signal images. This results in lower resolution. Further, this prior art system necessitates a complicated and expensive device for optically forming the index signal images on the target.

Accordingly, it is an object of this invention to provide an image pickup tube which is simple and relatively inexpensive to manufacture and which is particularly suited to be employed in a color television camera for producing color video signals of enhanced resolution and color purity.

In accordance with this invention, an image pickup tube has one end of its envelope closed by a transparent faceplate which, at its inner surface, carries a color filter made up of groups of stripe-shaped, parallel filter regions transmitting different wavelengths of light and being arranged in a repeating cyclic order of a predetermined pitch, a transparent glass plate is secured against the color filter and, at its side remote from the color filter, carries first and second comb-shaped electrodes which are insulated from each other and include respective transparent, elongated electrode elements extending parallel to the stripe-shaped filter regions and being interleaved to present an alternating cyclic order having a pitch equal to that of the filter regions, a photoconductive layer covers at least the electrode elements, and first and second output electrodes or terrhinals are connected with the respective first and second comb-shaped electrodes.

With the above image pickup tube according to this invention incorporated in a color television camera, the color filter is adopted to form on the photoconductive layer color separated images of an object in the field of view of the camera. Further, an alternating voltage may be applied to the first and second comb-shaped electrodes to provide a predetermined pattern of potential changes on the surface of the photoconductive layer of the pickup tube which is reproduced as an index signal. The index signal produced in this manner does not narrow the dynamic range of the image pickup tube and the resolution of the color video signal is not lowered. Further, the index signal, luminance signal and chrominance signal ar not derived from respective electrodes but are picked up in the form of one composite signal, so that even if crosstalk exists between the electrodes, color difference signals can be readily derived from a demodulator circuit, and accordingly a color video signal of good white balance can be obtained.

Since the index signal is obtained at the output of the pickup tube by supply an alternating voltage to the comb-shaped electrodes, which alternating voltage is preferably in synchronism with the line scanning period of the pickup tube, demodulation of the color video signal is easily accomplished. Further, if the color video signal is reproduced without the chrominance signal, the index signal may be simply obtained by adding to the output of the image pickup tube a signal produced by delaying the pickup tube output by one horizontal scanning period. In this manner, mixing of the index signal with the demodulated color video signal may be positively avoided.

Since the pitch of the repeating cyclic order of the color filter regions and the pitch of the alternating repeat of the interleaved elements of the comb-shaped electrodes are equal in the image pickup tube according to this invention, the chrominance signal and the index signal are in the same band, and hence the bands of the luminance signal and the chrominance signal can be widened to thereby provide a color vide signal with high resolution. In addition, with the image pickup tube according to the invention, the index signal and the chrominance signal can be derived from a common preamplifier and filter, so that no difference in the delay time between these signals is produced and accordingly a picture of excellent white balance can be obtained. Further, the index signal does not interfere with the chrominance signal, and hence the picture quality is not degraded.

Further, with the image pickup tube according to this invention, a simple optical system leading to a relatively inexpensive color television camera may be employed for focussing the image of an object to be televised onto the photoconductive layer which is in close proximity to the color filter formed on the face plate. So long as the filter regions of the color filter are substantially parallel to the elements of the comb-shaped electrodes, the relative positions thereof are not critical and hence adjustment of their relative positions during manufacture of the image pickup tube is easily accomplished.

The above, and other objects, features and advantages of the present invention will be apparent in the following detailed description of illustrative embodiments which is to be read in connection with the accompanying drawings, wherein:

FIG. 1 is a system diagram illustrating a color television camera of a type in which an image pickup tube in accordance with the present invention may be employed;

FIG. 2 is a perspective view, partly in cross-section, schematically showing the principal parts of the image pickup tube employed in the color television camera illustrated in FIG. 1;

FIGS. 3, 4A-4F, and 4A4C' are waveform diagrams, for explaining the operation of the camera shown on FIGs. 1 and 2;

FIG. 5 is a graph showing one example of a frequency spectrum for a color video signal produced by the color television camera of FIGS. 1 and 2;

FIG. 6 is a plan view showing the arrangement of the indexing electrodes in one image pickup tube according to this invention; and

FIG. 7 is a sectional view taken along the line 77 on FIG. 6, and showing the structure by which each of the indexing electrodes of the image pickup tube may be connected to the associated electric circuit.

Referring to FIGS. 1 and 2 in detail, it will be seen that an image pickup tube 2 according to this invention generally comprises a tube envelope 5 closed, at one end, by a face plate assembly 401 that includes a transparent faceplate 4 having a color filter F on its inner surface, a glass plate 3 against the inner side of filter F and having electrodes A and B on the inner surface of plate 3, and a photoconductive layer 1 covering at least the electrodes A and B on glass plate 3. An electron gun 11 is provided within tube envelope 5 for emitting an electron beam toward layer 1, and a deflecting coil 6, focusing coil 7 and alignment coil 8 are provided about tube envelope 5 for deflecting the electron beam so that the latter scans layer 1, and for focusing and aligning the electron beam, respectively. When image pickup tube 2 is incorporated in a color television camera, as shown, an image lens 9 of the camera is effective to focus onto photoconductive layer 1 through faceplate 4 an image of the object 10 in the field of view of the camera.

It will be apparent that the pair of index electrodes A (composed of elements A,,A ,...A,,...A,,) and B (composed of elements B,,B ...B,...B,,) are disposed adjacent the photoconductive layer 1 which may be formed, for example, of materials such as antimony trisulfide, lead oxide and the like. The electrodes A and B are transparent conductive layers, for example, formed of tin oxide including antimony, and they are arranged with their elements parallel and alternated, for example, in an order which may be A,,B,,A ,B ..A,,B,,....A,,,B,,. The electrodes A and B are shown respectively connected to terminals T and T for connection with external circuits. In this case, the electrodes A and B are disposed so that the longitudinal axes of their elongated elements may cross the horizon tal scanning direction of the electron beam.

The filter F which is separated from electrodes A and B by glass plate 3 is made up of red, green and blue color filter elements F,,,F and F arranged in a repeating cyclic order of F,,,F,;,F,,,F,,,F,,-,F,,....and disposed parallel to the length of the elements of electrodes A and B in such a manner that each triad of red, green and blue color filter elements F,,,F,,- and F may be opposite and corresponds to a pair of adjacent electrode elements A, and B,. So long as the elements of electrodes A and B and of optical filter F are aligned with each other in the longitudinal direction, that is, extend parallel to each other, and each triad of filter elements F,,, F,; and F,, has a pitch, that is extends over a lateral distance, that is equal to the pitch or lateral distance of the respective pair of electrode elements A, and B,, the relative lateral positioning of the color filter elements and the electrode elements is not critical.

In order to demonstrate the advantageous characteristics of the image pickup tube 2 according to this invention, the operation of such tube will be described in a color television camera having associated circuits which are shown schematically on FIG. 1 to include a transformer 12 provided with a primary winding 12a and a secondary winding 12b with a mid tap t,,. The end terminals 1, and t of the secondary winding 12b are respectively connected to terminals T of the image pickup tube 2. The primary winding 12a is connected to a signal source 13 which produces an alternating signal S, (FIG. 3) that is synchronized with the line scanning period of the image pickup tube 2. This alternating signal S, has a rectangular waveform with a pulse width equal to a horizontal scanning period H of the electron beam, for example, a pulse width of 63.5 microseconds, and a frequency which is one-half of the horizontal scanning frequency, namely, 15.75/2 KHz. The mid tap t of secondary winding 12b is connected to the input of a preamplifier 15 through a capacitor 14 and is supplied with a DC bias voltage of 10 to 50V from a power source B+ through a resistor R.

With such an arrangement, the electrodes A and B are alternately supplied with voltages higher and lower than the DC bias voltage for every horizontal scanning period, so that a striped potential pattern corresponding to the electrodes A and B is formed on the surface of the photoconductive layer 1. Accordingly, when the image pickup tube 2 is not exposed to light, electron beam scanning of layer 1 results in a signal S, corresponding to the rectangular waveform illustrated in FIG. 4A being derived, in a scanning period H,, at the mid tap t of the secondary winding 12b. When a DC bias voltage, for example, 30V, is supplied to the mid tap t of the secondary winding 12b and an alternating voltage 0.5V is impressed between the terminals T and T the current flowing across the resistor R varies by 0.05 microamperes and can be used as an index signal. The frequency of this index signal S, is determined by the width and interval of the elements of electrodes A and B, that is, by the pitch or lateral distance covered by each pair of electrode elements A, and B,, and by the horizontal scanning frequency of the electron beam which may be selected to provide the index signal S, with a frequency of, for example, 3.5 SMHz.

When a color separated image of the object 10 is focused on the photoconductive layer 1 by means of lens 9 and filter F, signals corresponding to the light intensity of the filtered red, green and blue components are produced in overlapping relation with the index signal S, in response to beam scanning of layer 1 to produce a composite signal S such as is illustrated in FIG. 4B, and in which the reference characters R,G and B respectively designate portions of the composite signal 8, corresponding to the red, green and blue color components. The composite signal S, is the sum of the luminance signal 8,, the chrominance signal S and the index signal 8,, namely S -Srl-S -l-S, The frequency spectrum of the composite signal 8,, as illustrated in FIG. 5, is determined by the width of the elements of electrodes A and B and of the optical filter F, and by the horizontal scanning period. That is, the composite signal 8,, in its entirety, is in a bandwidth of 6MHz and the luminance and chrominance signals Sy and S are respectively arranged in the lower and higher bands of that bandwidth. It is preferred to minimize overlapping of the luminance and chrominance signals S, and S and, if desired, it is possible to dispose a lenticular lens or the like in front of the image pickup tube 2. This optically lowers resolution and narrows the luminance signal band.

In the next horizontal scanning period H the voltage (the alternating signal) applied to the electrodes A and B is reversed in phase, in which case an index signal S, is produced, as depicted in FIG. 4A, which is opposite in phase to the index signal S, shown in FIG. 4A. Accordingly, a composite signal S is then supplied to the input side of the preamplifier 15, as shown in FIG. 4B, namely S =S +S S,.

Such a composite signal S (or S is supplied through the preamplifier to the process amplifier 16 for waveform shaping and/or gamma correction. Thereafter, the signal is applied to a low-pass filter 17 and a bandpass filter 18. As a result, the luminance signal Sy and a signal S =S +S,,, (FIG. 4C), or a signal S '=S S,,, (FIG. 4C) are respectively derived from the low-pass filter l7 and the bandpass pass filter 18. In the foregoing equations for S and S S and S,,, are low frequency components or fundamental components of the chrominance signal S, and the index signal 8,, respectively.

Since the pitch of each pair of electrode elements A, and B, of index electrodes A and B is equal to the pitch of each triad of filter elements F,,,F,,- and F,,, the repetitive frequencies of the index signal S, and the chrominance signal 8,; are equal to each other, and the separation of those signals S, and S may be achieved in the following manner without using a filter.

Reference numeral 19 indicates a delay circuit, for example, an ultrasonic delay line, by means of which the signal S =S +S,, (or (S,,=S -S,,,) derived from the bandpass filter 18 is delayed by one horizontal scanning period 1H. The signals S =S +S,,, (or S '=S S,, in a certain horizontal scanning period H, and the signal S =S -S, (or S =S +S,, in the subsequent horizontal scanning period H which are derived from the delay circuit 19 and the bandpass filter 18 are supplied to an adder circuit 20 to be added together, providing as an output a chrominance signal 28 such as is depicted in FIG. 4D. In this case, the contents of chrominance signals in adjacent horizontal scanning periods are so similar that they can be regarded as substantially the same. Further, it is also possible to delay the signal from the bandpass filter 18 by three or five horizontal scanning periods due to their similarity.

These signals S =S ,,+S,, (or S =S S, and S '=S ,,S,,, (or S =S ,,iS,, in the horizontal scanning periods H, and H are also applied to a subtraction circuit 21 to achieve a subtraction (S ,,S,,,)(S ,,+S,,,) [or (S +S,,,)(S,-, S,,,)]to derive therefrom an index signal 2S',, (FIG. 4E) or 2S,, (not shown). The resulting index signal 2S, or 2S,,,, is fed to a limiter circuit 22 to render its amplitude uniform, and thereby forming an index signal 2S, (or 28,) as depicted in FIG. 4F.

The index signal 2S, or 25,) thus obtained is reversed in phase at every horizontal scanning period, so that the signal 2S, is corrected in phase through the use of a change-over switch 23 (an electronic switch in.

practice) having fixed contacts 23a and 23b and a movable contact 230. The output side of the limiter 22 is directly connected to one fixed contact 23a of the change-over switch 23 and to the other fixed contact 23b through an inverter 24. The change-over switch 23 is constructed so that its movable contact 23c makes contact with the fixed contacts 23a and 23b alternately for every horizontal scanning period in synchronism with the alternating signal S, impressed on the primary winding 12a of the transformer 12 to thereby derive the index signal 28, from the movable contact 230 at all times.

The chrominance signal S derived from the adder circuit 20 is supplied to synchronous detectors 25,26 and 27.. The index signal 5,, is supplied to the synchronous detector 25 through a phase shifter 28 which adjusts the phase of the index signal to that of the red signal in order to produce a color difference signal R-Y at the output of the detector 25. In a similar manner the output signal from the phase shifter 28 is supplied to the synchronous detector 26 through a phase shifter 29 to produce a color difference signal G-Y at the output of the detector 26 and the output signal from the phase shifter 29 is supplied to the synchronous detector 27 through a phase shifter 30 to produce a color difference signal B-Y at the output of the detector 27. The phase shifters 29 and 30 each change the phase of the input thereto by 120. These color difference signals and the luminance signal S, are applied to a matrix circuit 31 to derive color signals S,,,S and S at its terminals T T G and T respectively. The color signals thus obtained may be suitably processed to produce color television signals for the NTSC system and other various systems.

Referring now to FIGS. 6 and 7, it will be seen that, in a preferred construction of the image pickup tube 2 according to this invention for use in the color television camera system of FIGS. 1 and 2, a transparent conductive layer, for example, of tin oxide, is deposited on the entire area of one surface of the thin glass plate 3 and is then subjected to photoetching to remove selected portions of that conductive layer so that the remaining portions of the latter form the two interleaved, comb-shaped indexing electrodes A and B and a surrounding electrode C (FIG. 6). The surface of plate 3 facing away from electrodes AB and C thereon is bonded, as by adhesive, to the glass face plate 4 which has the striped color filter F formed thereon. Holes 32 (FIG. 6) are bored through plates 3 and 4 at locations within the spines or bus-bar portions of electrodes A and B and each receive a conductive post 33 (FIG. 7), for example, of copper, which is sealed in the respective hole 32 by an indium bushing 34 which is also intended to establish electrical contact between the post 33 and the respective indexing electrode A 'or B. The photoconductive layer 1 is then applied over the entire surface of plate 3 'having the electrodes A,B and C thereon.

The face plate assembly 401, constructed as above, is then secured on the front end of the tube envelope 5 by means of a conductive ring 35 and an intervening seal 36 of indium which extends onto the electrode C for electrically connecting the latter with conductive ring 35. Since the resistance of photoconductive layer 1 is very high, that layer 1 can extend onto electrode C, as shown, without disturbing the operation of the image pickup tube.

In employing the image pickup tube having the construction described above with reference to FIGS. 6 and 7 in the color television camera system of FIG. 1, the posts 33 associated with electrodes A and B are respectively connected to terminals T and T on FIG. 1. Further, if desired, electrode C may be grounded, or

supplied with a bias potential equal to that applied to I electrodes A and B, by way of the conductive ring 35 so as to prevent the storage of any unwanted charge on the faceplate assembly as a result of the impingement of the electron beam thereon. Of course, the mentioned unwanted charge also tends to be discharged from the electrode C to the electrodes A and B when the photoconductive layer 1 extends onto the electrode C, as shown.

Although an illustrative embodiment of the invention has been described in detail herein with reference to the accompanying drawings, it is to be noted that the invention is not limited to that precise embodiment, and that various changes and modifications may be effected therein by one skilled in the art without departing from the scope or spirit of the invention.

What is claimed is:

1. In an image pickup tube having an envelope closed, at one end, by a transparent faceplate, the combination of a color filter on theinner surface of said faceplate including triads of stripe-shaped, parallel filter regions transmitting respective different wavelength bands of light and being arranged in a repeating cyclic order of a predetermined pitch, a transparent glass plate secured against the inner side of said color filter, first and second comb-shaped electrodes on said glass plate, said first and second comb-shaped electrodes being insulated from each other and including first and second transparent, elongated electrode elements, respectively, which extend parallel to said stripe-shaped filter regions and are interleaved to present an altemating cyclic order of said first and second electrode elements which has a pitch substantially equal to said pitch of the repeating cyclic order of the filter regions so that, for each of said triads of filter regions, there is a pair of said first and second electrode elements, a photoconductive layer at least on said transparent elongated electrode elements, and first and second output electrodes respectively connected with said first and second comb-shaped electrodes.

2. An image pickup tube according to claim 1, in which said first and second output electrodes are constituted by respective conductive posts extending from said first and second comb-shaped electrodes through said glass plate and said faceplate to the exterior of the latter.

3. An image pickup tube according to claim 1, in which said glass plate has an additional electrode thereon in surrounding relation to said pair of combshaped electrodes. 

1. In an image pickup tube having an envelope closed, at one end, by a transparent faceplate, the combination of a color filter on the inner surface of said faceplate including triads of stripe-shaped, parallel filter regions transmitting respective different wavelength bands of light and being arranged in a repeating cyclic order of a predetermined pitch, a transparent glass plate secured against the inner side of said color filter, first and second comb-shaped electrodes on said glass plate, said first and second comb-shaped electrodes being insulated from each other and including first and second transparent, elongated electrode elements, respectively, which extend parallel to said stripe-shaped filter regions and are interleaved to present an alternating cyclic order of said first and second electrode elements which has a pitch substantially equal to said pitch of the repeating cyclic order of the filter regions so that, for each of said triads of filter regions, there is a pair of said first and second electrode elements, a photoconductive layer at least on said transparent elongated electrode elements, and first and second output electrodes respectively connected with said first and second comb-shaped electrodes.
 2. An image pickup tube according to claim 1, in which said first and second output electrodes are constituted by respective conductive posts extending from said first and second comb-shaped electrodes through said glass plate and said faceplate to the exterior of the latter.
 3. An image pickup tube according to claim 1, in which said glass plate has an additional electrode thereon in surrounding relation to said pair of comb-shaped electrodes. 